Abstract:

Objective

To explore the effect of the change of Ca and P concentration in the electrolyte on the micro-mechanical properties of the titanium alloy coating formed by microarc oxidation （MAO） technique.

Methods

Thirty two disc-shaped Ti-6Al-4V specimens （10 mm in diameter and 1 mm in thickness） were equally divided into 4 groups.The surfaces were treated by MAO technique in electrolytic solution containing calcium acetate （CA） and β-glycerol phosphate disodium salt pentahydrate （β-GP）.The concentration of β-GP was fixed at 0.02 mol/L，while the concentrations of CA were set at 0.05-0.3 mol/L respectively for the 4 testing groups.The Ca/P ratios of the surface MAO coatings were detected by energy dispersive X-ray analysis（EDX）.The micro hardnesses and elastic moduli were measured by a nano-indentation tester.

Results

When the CA concentration was increased from 0.05 to 0.3 mol/L in the electrolyte，the Ca/P ratios of the MAO coating increased accordingly from 0.52±0.02， 1.23±0.05， 1.75±0.10 to 2.44±0.05.The elastic moduli and the hardnesses of the 4 groups of MAO coating were（56.11±8.22）GPa， （48.46±9.74）GPa， （32.07±7.07）GPa， （28.19±6.94）GPa and （3.13±0.78）GPa， （2.56±0.85）GPa，（1.49±0.68）GPa，（0.68±0.27）GPa respectively.

Conclusions

The Ca/P concentration of the electrolyte has a significant effect on the micro-mechanical properties of the MAO coating of titanium alloy.The micro-elastic modulus and micro-hardness of the MAO coating decrease with the Ca/P ratio.

Key words: Titanium alloy, Coating, Mechanical property, Nano-indentation, Micro-arc oxidation